An electrocardiograph is an instrument to be applied to the human body for the purpose of making a gram or recorded line for indicating the operations of the heart, such as the expansion and contraction of the heart muscle, which is accompanied by electric currents. The electrocardiograph records the changes of electrical potential occurring in the form of a tracing on a paper chart or strip divided into blocks 1.0 mm square, which are representative of units of time.
The normal heart rate of an adult is considered to lie between 60 and 100 beats/minute. Slower rates often enable the emergence of extra, irregular beats and a transition to a very rapid heart rate and fast heart rates, often described as palpitations of the heart, may follow irregular beating and produce weakness, fatigue, anxiety and faintness. The ultimate danger from all types of alterations in the rhythm of the heartbeat or cardiac arrhythmias is their possible progression to cardiac arrest and sudden death.
The great variety and number of cardiac rhythmic disburbances and diseased rhythmic mechanisms point up the magnitude of the diagnostic problem facing the physician who must make a definitive diagnosis before selecting a medication to treat the arrhythmia. Also, with the variety of anti-arrhythmic medications available, each possessing its own mode of action and nuance of effect, precise diagnosis of the arrhythmia is most important for selection of optimum therapy.
In view of the magnitude of the problem of accurate diagnosis and matching the medication to the arrhythmia, the need for a diagnostic tool or aid for the study of arrhythmias recorded on the conventional electrocardiographic (ECG) chart or strip would appear to be evident.
Heretofore, various scales for determining the average heart rate based on 2-beat or 3-beat counts have been available, but these have no applicability to the diagnosis of arrhythmias. A device generally used is a caliper or divider, an instrument which can be adjusted to the interval of a single heart beat. However, it is limited in use to examining one beat at a time and then comparing one beat to the next. Thus, the caliper does not provide for simultaneous analysis of a group or sequence of beats so that the rhythm created by the sequence of beats could be observed and any departure from regularity would be immediately revealed.
Moreover, various time intervals on the ECG waveform are of importance, such as heart rate, cycle duration, the time from onset of the P-wave to onset of the QRS wave (PR interval), and the time from onset of the QRS wave to the end of the T-wave (QT interval). For the physician to evaluate these intervals for abnormalities requires several measurements and corrections made by calculations or use of reference tables, none of which steps are quick or convenient.
Thus, the development of a device or diagnostic tool which would enable analysis of a group or sequence of beats simultaneously so as to provide ready means for determining the regularity of the rhythm of the heart beats would not only be highly desirable but of significant importance. Furthermore, the desirability of such a device that could also combine means for conveniently diagnosing other characteristics of the ECG waveform, must be obvious.